Remember this? The last time Apple offered a public beta was in 2000. The preview version of the first iteration of OS X came on a disk with a handy how-to guide.

If you're lucky enough to be one of those beta testers, congratulations! Here's a quick rundown of what you should know and keep in mind about the beta as you start poking around Apple's latest operating system. (The final version is due out this fall.)

1. The beta is a work in progress

First and foremost, keep in mind that this isn't the official release of the software; Apple is still testing and tweaking Yosemite. That means it may not function as expected. Some features may be completely absent or could differ from what Apple showed off during its WWDC keynote in June -- and some features may look very different in the final release. Even some of the standard features available in Mavericks or earlier versions of OS X may be missing, nonfunctional or just different. That's because a major OS upgrade, particularly one like Yosemite that makes major changes to the user experience, often involves updating or altering existing functions, including core components that aren't visible to most users.

2. A public beta isn't the same as a developer preview

Apple has already released beta versions of Yosemite to members of its Mac developer program. The most recent was made available to them earlier this week, with revisions arriving roughly every two weeks. In fact, the version of Yosemite offered as the public beta has a different build number (it's one digit higher) than the version developers received on Monday.

Apple's FAQ for the Yosemite beta indicates that beta testers may not see updates at the same rate as developers. There's a good chance this means beta testers will see less frequent updates than developers.

Other differences are likely to include support, resources or some functionality. Developers are receiving the betas to build and/or test apps running under Yosemite and make changes if needed. Beta testers are being asked to provide feedback. Those are rather different roles, and developers aren't likely to provide the type of feedback -- general user interface (UI) issues or consumer-oriented feature requests -- that Apple is looking for from public beta testers.

3. Explore Yosemite and report back to Apple

Apple's goal with this program is largely to solicit feedback about Yosemite, particularly about its new UI. If there are things that aren't working, are confusing, seem like they should work better, or that you really dislike, you should report them to Apple using the Feedback Assistant that's included. During the public beta prior to the release of OS X in 2000, Apple made several changes based on user feedback -- the most obvious was restoring the Apple menu in the shipping version of OS X, which had been replaced with an Apple logo in the middle of the menu bar.

Although Apple suggests simply using your Mac as you normally would, you should also explore a bit. The advantage here for Apple is that you'll play with more Yosemite features and potentially provide more useful feedback. You also might discover new (or existing) features that you might not have considered using otherwise.

You should also report issues with third-party software if it seems that Yosemite has broken something in existing apps. That gives Apple the ability to look at underlying problems affecting those particular apps and potentially others.

4. Don't install Yosemite on a mission-critical Mac

You shouldn't install the Yosemite beta on a Mac that you need for important work. There's a very real possibility that you may encounter a serious problem -- like losing important data, having some key apps stop working or having your entire Mac be disabled.